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dd

/dee-dee/ [UNIX from IBM JCL] vt. Equivalent to
cat or BLT. This was originally the name of a UNIX copy
command with special options suitable for block-oriented devices.
Often used in heavy-handed system maintenance, as in "Let's
`dd' the root partition onto a tape, then use the boot PROM to
load it back on to a new disk". The UNIX `dd(1)' was
designed with a weird, distinctly non-UNIXy keyword option syntax
reminiscent of IBM System/360 JCL (which had an elaborate DD `Data
Definition' specification for I/O devices); though the command
filled a need, the interface design was clearly a prank. The
jargon usage is now very rare outside UNIX sites and now nearly
obsolete even there, as `dd(1)' has been deprecated for a
long time (though it has no exact replacement). Replaced by
BLT or simple English `copy'.